an extinct carnivorous mammallike reptile, of the genus Dimetrodon, dominant in North America during the Permian Period, up to 10 ft. (3.1 m) long and usually bearing spinal sails
Word origin
[‹ NL (1878), equiv. to Gk dímetr(os) having two measures ( see dimeter) + odo᷇n tooth; appar. so named in reference to the large size of the anterior incisors relativeto the other teeth]